Molten metal-containing vessel, and methods of producing same

ABSTRACT

Exemplary embodiments of the invention provide a vessel for containing or conveying molten metal therein. At least part of the outer surface of the vessel incorporates a web of metal wires embedded in the surface, the wires being mutually overlaid with openings formed therebetween. The refractory material penetrates into the openings. The web may comprise woven metal wires or non-woven wires or both. The web imparts resistance to cracking (or containment of cracks, once formed) and/or resistance to molten metal leakage if cracks develop. The invention also provides metal containment structures containing such vessels, and methods of producing the same.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a division of U.S. patent application Ser. No.12/928,356 filed on Dec. 8, 2010, now U.S. Pat. No. 9,498,821, whichclaims the benefit of U.S. provisional patent application Ser. No.61/283,906 filed on Dec. 10, 2009, the entire contents of both of whichare specifically incorporated herein by this reference.

BACKGROUND OF THE INVENTION

I. Field of the Invention

This invention relates to molten metal containment structures includingrefractory or ceramic vessels used for conveying, treating and/orholding molten metals. More particularly, the invention relates to suchvessels and sections thereof.

II. Background Art

Metal containment structures such as launders, runners, etc., are oftenrequired during casting operations and the like to convey molten metalfrom one location, e.g. a metal melting furnace, to another location,e.g. a casting mold or casting table. In other operations, metalcontainment structures are used for metal treatments, such as metalfiltering, metal degassing, metal transportation, or metal holding.Metal-contacting vessels, such as troughs, containers, ladles and thelike, used in such structures are generally made from refractorymaterials, and especially ceramic materials, that are resistant to hightemperatures and to degradation by the molten metals to which they areexposed. Sometimes, such structures are provided with sources of heat toensure that the molten metals do not cool unduly or solidify as they arecontained within or conveyed through the vessels. The source of heat maybe electrical heating elements positioned adjacent to the vessels orenclosures conveying hot fluids (e.g. combustion gases) along the inneror outer surfaces of the vessels.

Refractory vessels used in such structures are subjected to thermalcycling, i.e. significant changes of temperature, when molten metal isbeing conveyed or when additional heating is applied, or when the vesselsections are idle or allowed to cool. Thermal cycling can cause cracksto form in the refractory material from which the vessels or vesselsections are made. The cracks propagate with time and may eventuallybecome so large and deep that molten metal leaks from the vessels. Whenthis happens, the vessels thus-affected must be repaired or replaced,and often the service lives of such components are quite short. There istherefore a need for ways of extending the effective service lives ofmolten metal-contacting vessels and sections thereof, and ways ofpreventing or minimizing crack formation and leakage of molten metalfrom such vessels.

U.S. Pat. No. 2,301,101, which issued to Lewis T. Welshans on Nov. 3,1942, discloses a refractory hot top for a casting mold having wire meshembedded in its walls, but this there is no disclosure of such use intrough sections.

U.S. Pat. No. 5,505,893, which issued to Charles W. Connors, Jr. on Apr.9, 1996 discloses an open mesh screen used in molding a refractorylining of a trough. However, the screen is removed or dissolved awayafter the trough has been completed.

Despite these disclosures, there is still a need for improved vesselsections and improved methods of making the same.

SUMMARY OF THE EXEMPLARY EMBODIMENTS

An exemplary embodiment provides a vessel for contacting molten metal,the vessel comprising a body of refractory material having a cavity forcontaining or conveying molten metal and an outer surface having a webof metal wires embedded therein. The wires of the web are overlaid withrespect to each other with openings formed between the wires into whichthe refractory material penetrates.

Another exemplary embodiment provides a molten metal containmentstructure comprising a vessel as defined above, and a metal casing atleast partially surrounding the vessel.

According to yet another exemplary embodiment, a method of making areinforced refractory vessel or vessel section is provided. The methodinvolves providing a mold having the intended shape of the vessel orvessel section, creating a slurry of refractory material capable offorming a cast refractory body, lining at least one internal surface ofthe mold with a web of metal wires, the wires being overlaid withopenings formed therebetween, introducing the slurry into the mold whilecausing the slurry to penetrate the openings, allowing the slurry to setto form a vessel or vessel section incorporating the web at an outersurface thereof, and removing the vessel or vessel section from themold. The mold may be vibrated and/or pressurized before the slurry setsor hardens to facilitate penetration of slurry into the openings of theweb.

Yet another exemplary embodiment provides an alternative method ofmaking a reinforced refractory vessel. The alternative method involvesproviding a vessel made of a refractory material and having an externalsurface, and adhering a web to the external surface, wherein the webcomprises metal wires having openings therebetween, and wherein the webis adhered to the external surface by means of a refractory adhesivethat is infiltrated into the web through the openings.

Preferably, the vessel is shaped and dimensioned for use as an articleselected from the following: an elongated metal-conveying trough havinga channel formed therein, a container for a molten metal filter, acontainer for a molten metal degasser, a crucible, and the like.

The vessel of the exemplary embodiments is made of a refractorymaterial. The term “refractory material” as used herein to refer tometal containment vessels is intended to include all materials that arerelatively resistant to attack by molten metals and that are capable ofretaining their strength at the high temperatures contemplated for thevessels during normal use, e.g. the temperatures of molten metals. Suchmaterials include, but are not limited to, ceramic materials (inorganicnon-metallic solids and heat-resistant glasses) and non-metals. Anon-limiting list of suitable materials includes the following: theoxides of aluminum (alumina), silicon (silica, particularly fusedsilica), magnesium (magnesia), calcium (lime), zirconium (zirconia),boron (boron oxide); metal carbides, borides, nitrides, silicides, suchas silicon carbide, nitride-bonded silicon carbide (SiC/Si₃N₄), boroncarbide, boron nitride; aluminosilicates, e.g. calcium aluminumsilicate; composite materials (e.g. composites of oxides andnon-oxides); glasses, including machinable glasses; mineral wools offibers or mixtures thereof; carbon or graphite; and the like.

The vessel of the exemplary embodiments is normally intended forcontaining molten aluminum and aluminum alloys, but may be used forcontaining other molten metals, particularly those having similarmelting points to aluminum, e.g. magnesium, lead, tin and zinc (whichhave lower melting points than aluminum) and copper and gold (that havehigher melting points than aluminum). Preferably, for use with aparticular molten metal intended to be contained or conveyed, the metalchosen for the wires of the metal web should be unreactive with thatparticular molten metal, or at least sufficiently unreactive thatlimited contact with the molten metal does not cause excessive erosion,dissolution or absorption of the mesh. Titanium is a good choice for usewith molten aluminum and aluminum alloys, but has the disadvantage ofhigh cost. Less expensive alternatives include, but are not limited to,Ni—Cr alloys (e.g. Inconel®) and stainless steel.

The vessel may form part of a metal containment structure having anouter metal casing, and the structure may be provided with a heater forthe molten metal. Heated structures of this kind are disclosed in U.S.Pat. No. 6,973,955 issued to Tingey et al. on Dec. 13, 2005, or pendingU.S. patent application Ser. No. 12/002,989, published on Jul. 10, 2008under publication no. U.S. 2008/0163999 to Hymas et al. (the disclosuresof which patent and patent application are specifically incorporatedherein by this reference).

BRIEF DESCRIPTION OF THE DRAWINGS

Exemplary embodiments are described in the following with reference tothe accompanying drawings, in which:

FIG. 1 is a perspective view of a trough section according to oneexemplary embodiment;

FIG. 2 is a lateral cross-section of the trough section of FIG. 1 takenon the line II-II of FIG. 1;

FIG. 3 is a side view of a reinforcing web used in the trough section ofFIGS. 1 and 2;

FIG. 4 is plan view of the reinforcing web of FIG. 3;

FIG. 5 is a plan view of a woven layer forming part of the reinforcingweb of FIGS. 3 and 4;

FIG. 6 is a plan view of a non-woven layer forming another part of thereinforcing web of FIGS. 3 and 4;

FIG. 7 is an enlarged cross-section of part of a metal-conveying troughsection close to a sidewall thereof showing the position of areinforcing web according to FIGS. 3 to 6;

FIG. 8 is an end view of a metal containment structure for conveyingmolten metals incorporating a trough section as shown in FIGS. 1 and 2;and

FIG. 9 is a vertical transverse cross-section of a trough sectionsimilar to that of FIG. 2, but showing a further exemplary embodiment.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

FIGS. 1 and 2 show a metal containment vessel in the form of a metalconveying trough or trough section 10 according to one exemplaryembodiment. The vessel will be referred to below as a trough sectionbecause metal conveying troughs usually consist of two or more suchsections laid end-to-end, although a functional trough may consist ofjust one such section. Normally, the trough section(s) would be heldwithin an outer metal casing of a molten metal containment structure (anembodiment of which is described later in connection with FIG. 8) toprovide physical protection for the trough section(s) and to keep thetrough sections mutually aligned when there is more than one. Heatingmeans (not shown) may also be provided to help keep the molten metal ata suitable temperature as it is conveyed through the trough section(s).

The illustrated trough section 10 has a body 11 made of a refractorymaterial that is resistant to high temperatures and to attack by themolten metal to be conveyed through the trough section. Examples ofparticularly preferred materials that may be used for the body 11include ceramics such as alumina, silicon carbide (e.g. nitride-bondedsilicon carbide), aluminosilicates, fused silica, or combinations ofthese materials. Of course, other refractory materials, e.g. any ofthose mentioned earlier, may be used for the body. The body 11 has anouter surface 18 extending over opposed side walls 12, a bottom wall 13,opposed longitudinal ends 14 and an upper wall 15. An elongated U-shapedmetal-conveying channel 16 projects downwardly into the body 11 from theupper wall 15 and extends from one longitudinal end 14 of the body tothe other. As illustrated in FIG. 2, the trough section, in use,contains molten metal up to a depth represented by a horizontal level17, shown as a dotted line, and conveys the molten metal from one end ofthe trough section to the other. The level 17 represents a height abovewhich an upper surface of molten metal conveyed through the troughsection does not rise during normal use of the trough section.

The side walls 12 and bottom wall 13 are shown as planar but may, ifdesired, have a contoured shape and/or, in the case of the side walls, adegree of slope relative to the vertical. These walls are provided witha web 20 of metal wires embedded in the outer surfaces thereof. This webis shown in more detail in FIGS. 3 to 6 of the accompanying drawings inisolation from the refractory material of the body 11. It will be seenfrom the side view of FIG. 3 that the web 20 of this exemplaryembodiment is made up of two distinct sections, i.e. a woven metalmatrix 21 and non-woven matted (felt-like) metal matrix 22. These twosections are firmly attached together (e.g. by sintering or welding) sothey act as a single unified porous web 20. The woven matrix 21 (shownin isolation in FIG. 5) is formed of spaced-apart warp fibers andspaced-apart weft fibers interwoven together to leave openings betweenthe fibers preferably having an average size (width on each side ordiameter) in the range of 0.5 to 10 mm, more preferably 1 to 10 mm, andeven more preferably 1 to 5 mm. If the openings are made too small, somerefractory materials may not penetrate into the openings fully and thewoven layer 21 may undesirably create a broad shear plane against whichthe refractory material may be free to move. If the opening size is muchgreater than about 10 mm, there may not be enough wire density in someembodiments to effectively hold the refractory in place. It should benoted, however, that openings having widths outside the stated rangesmay be effective for some refractory materials, and for some metals usedfor the wires, so simple testing may be employed to establish theoptimum size range for any particular refractory material used for thebody 11 of the trough section. The refractory material penetrates theopenings of the woven matrix to form a unitary structure with the metalweb 20. This provides the trough section with an effective reinforcementto prevent cracks from forming or to limit the propagation or wideningof cracks once formed in the trough. A single layer of the woven matrix21 is preferred, as shown, but a plurality of woven layers mayalternatively be used, particularly if such layers are firmly attachedtogether, e.g. by sintering or welding. An example of a suitable wovenmatrix for one particular embodiment is a #2 wire screen which hasopenings of about 7 mm in width and wires of about 14 mm in diameter.The woven matrix may be used alone, but preferably it is employed incombination with a non-woven matrix 22 as described below.

The non-woven matrix 22 (shown in isolation in FIG. 6) consists of wirestrands laid over each other in a random fashion with openings formedbetween the strands. The openings between the strands may be similar insize to those between the wires of the woven matrix, but are preferablysmaller. The openings preferably range in size from about 5 μm to 10 mm,but more preferred maximum sizes are 5 mm, 1 mm, 500 μm, 450 μm, 400 μm,350 μm, 300 μm, 250 μm, 200 μm and 150 μm. Most preferably, the averageopening size is in the range of 50 to 150 μm, and generally around 100μm (±25%), although smaller and larger opening sizes may be effective inparticular embodiments. The opening size of the non-woven matrix 22 ispreferably large enough to allow effective penetration by the refractorymaterial used to form the body of the trough section, but preferablysmall enough that molten metal will not easily penetrate through thematrix should a crack develop in the adjacent trough section. Thenon-woven matrix 22 is preferably made up of many metal wires overlyingeach other and compressed together to form a relatively thick layer sothat, should molten metal begin to penetrate this layer, it must followa tortuous or convoluted path to penetrate completely through the metalmatrix, which again makes full penetration unlikely. In someembodiments, the non-woven matrix 22 may be used alone to provideresistance to metal penetration should a crack develop in the troughsection, but it is preferably used in combination with the woven matrix21 as shown and described above, so that a combination of strengtheningand resistance to metal penetration can be obtained. When the openingsize of the woven matrix is larger than the opening size of thenon-woven matrix, a combination of good reinforcement and resistance tometal penetration may be obtained. While the woven matrix is generallypreferred for reinforcement and the non-woven matrix is preferred forimparting resistance to metal penetration, these roles may be reversed,if desired, by providing the non-woven matrix with larger openings thanthe woven matrix.

One section, and preferably both sections, of the web 20 are preferablymade of a metal that is resistant to attack by, and not easily wettedby, the molten metal to be conveyed through the trough. This makes itless likely that molten metal will penetrate the metal web should acrack develop. Suitable metals include, but are not limited to,titanium, Ni—Cr alloys (e.g. Inconel®), stainless steel, titanium andother metals or alloys not easily dissolved by the molten metal beingconveyed. However, for the web 20, it has been found most advantageousto use a two layer material sold under the trade name G-mat® by MicronFiber-Tech of 230 Springview Commerce Dr., Suite 100, Debary, Fla.32713, USA. This product has a structure as shown in FIGS. 3 to 6 andcan withstand high heat and is made of a special Fe—Cr—Al-M alloy (whereM represents a proprietary ingredient).

The metals used for the wires of each web matrix 21 and 22 are normallythe same, but different metals may be used, if desired, e.g. to provideone matrix with more resistance to metal penetration and the other withmore strength for reinforcement of the refractory material.

The thickness of the wires used for the different matrices 21 and 22 maybe the same but they preferably differ, with thicker wires being usedfor the woven matrix 21 (for greater strength) and thinner wires usedfor the non-woven matrix 22 (to provide a more convoluted path forpenetrating molten metal). Examples of wire thicknesses are 0.0002 to0.0003 inch for the non-woven matrix 22 and 0.006 to 0.007 inch(diameter) for the wires of the woven matrix 21. However, thesethicknesses are just examples and should not be considered essential forproper effectiveness of the resulting metal webs. If the trough sectionis to be used in a heated molten metal distribution structure, the web20 should preferably have a high thermal conductivity to allowpenetration of the heat. However, almost any suitable metal for the webwould have a suitable thermal conductivity to facilitate the transfer ofheat from the heating means to the molten metal within the channel ofthe trough section.

FIG. 7 is an enlarged cross-section of a part of a trough section of thesame embodiment showing the structure of the body 11 adjacent to theouter side surface 18 at side wall 12. It will be seen that therefractory material of the body 11 has penetrated through both the websections and forms a part of the outer wall 12 of the trough section. Inthis embodiment, the non-woven matrix 22 is positioned closest to theoutside surface 18 and the woven matrix 21 is buried more deeply in therefractory material of the body 11. The non-woven matrix 22 resistspenetration of molten metal to the outer surface 18 of the troughsection should a crack develop, and the woven-matrix 21 providesstructural reinforcement and makes the formation and widening of such acrack less likely. Some of the wires of the non-woven matrix 22 may bevisible on the outer surface 18 but the section preferably hasrefractory material of the trough body 11 embedded therein. While it ispreferred to locate the woven matrix 21 further away from the surface 18than the non-woven matrix 22, as shown, this arrangement may be reversedif desired, i.e. the woven matrix 21 may be positioned closer to thesurface 18 than the non-woven matrix 22.

It is preferable to locate the web 20 exactly at (immediately beneath)the outer surface 18 of refractory material, as shown. A deeper positionwithin the body 11 of refractory material would cause the web 20 todivide the wall of the body 11 into two unreinforced (refractory-only)zones on each side of the web, which could reduce the strength andcrack-resistance of the wall. It is therefore considered better toposition the web exactly at the surface and to keep the refractory-onlyparts of the walls of the trough section as thick as possible.Furthermore, burying the web 20 more deeply creates two possible shearplanes along which the refractory may separate from the web, instead ofjust one in the embodiment as illustrated.

The web 20 is preferably incorporated into all parts of the outersurface 18 of the trough section below the horizontal level 17 (see FIG.2) corresponding to the maximum intended surface height of the metalwithin the channel 16, but is more preferably incorporated into allparts of the sidewalls 12 and the bottom wall 13, as shown. Cracks tendto form in the trough section at the top, so reinforcement adjacent thetop is desirable. There is generally no need, however, to incorporatethe matrix into the top wall 15 of the trough section.

Trough sections of the kind described above come in various sizes. Oneexample has a length of 665 mm, a width of 204 mm and a height of 365mm. Any size of trough section can be provided with an embedded web 20according to exemplary embodiments of the present invention.

As mentioned earlier, the trough section 10, which is an example of avessel for containing or conveying molten metal, may be included in ametal containment structure such as a metal-conveying launder, e.g. asshown in FIG. 8. In this exemplary embodiment, the trough section 10 isheld within a metal casing 30 for support and protection. The interiorof the casing may be provided with heating means (not shown) and/orthermal insulation.

FIG. 9 shows another embodiment of the vessel in which a trough section10 has a completely enclosed channel 16 extending from one longitudinalend to the other. The channel may be tubular (circular in cross-section)as shown, but may alternatively be of any cross-sectional shape, e.g.oval, asymmetrically round or polygonal. The web 20 extends along thebottom wall 13 of the trough and to a height at the sidewalls 12 that isabove horizontal level 17, i.e. the predicted maximum height of themolten metal conveyed through the channel. However, the web 20 mayextend all around the outer surface 18 of the trough section, ifdesired.

Trough sections of the above kinds and other refractory vessels andparts thereof having embedded metal webs may be made by casting a slurryof refractory particles in a mold of desired shape having a layer of themetal web 20 held against one or more sides of the mold that will formsidewalls or the bottom wall surfaces. The slurry may formed from aliquid (e.g. water or colloidal silica) and a refractory mix (rangingfrom fine powder to larger particulate). The slurry is preferablyformulated to provide optimal mold filling and penetration into theopenings of the web 20, as well as having a short drying time. Theslurry penetrates the metal web before it sets to form the solid body ofthe trough section. Desirably, the mold is vibrated and/or pressurized(e.g. by introducing the slurry under pressure) as the slurry isintroduced and before the slurry sets in order to facilitate thepenetration of the slurry into and through the layers of the metalreinforcement. The trough section is then removed from the mold, driedand normally fired to form a tough refractory solid body with the web 20of metal wires still in place and embedded in the refractory surfaces.

An alternative method of formation involves adhering the web 20 with arefractory adhesive to an outer surface of a pre-formed vessel or vesselsection made entirely of refractory material. The refractory adhesivepenetrates the web of metal wires and, once solidified, has the samestructure at the surface as the embodiments discussed above. However,there may be an increased likelihood that the web will become detachedfrom the remainder of the refractory material during crack formation orupon thermal cycling so this method is less preferred than the onediscussed above, but remains a useful way of modifying pre-formed troughsections to improve their properties, such as resistance to metalleakage.

In the above embodiments, the vessel has been shown as an elongatedmolten metal trough or trough section of the kind used in molten metaldistribution systems used for conveying molten metal from one location(e.g. a metal melting furnace) to another location (e.g. a casting moldor casting table). However, according to other exemplary embodiments,other kinds of metal containment and distribution vessels may employed,e.g. those designed as an in-line ceramic filter (e.g. a ceramic foamfilter) used for filtering particulates out of a molten metal stream asit passes, for example, from a metal melting furnace to a casting table.In such a case, the vessel includes a channel for conveying molten metalwith a filter positioned in the channel. Examples of such vessels andmolten metal containment systems are disclosed in U.S. Pat. No.5,673,902 which issued to Aubrey et al. on Oct. 7, 1997, and PCTpublication no. WO 2006/110974 A1 published on Oct. 26, 2006. Thedisclosures of the aforesaid U.S. patent and PCT publication arespecifically incorporated herein by this reference.

In another exemplary embodiment, the vessel acts as a container in whichmolten metal is degassed, e.g. as in a so-called “Alcan compact metaldegasser” as disclosed in PCT patent publication WO 95/21273 publishedon Aug. 10, 1995 (the disclosure of which is incorporated herein byreference). The degassing operation removes hydrogen and otherimpurities from a molten metal stream as it travels from a furnace to acasting table. Such a vessel includes an internal volume for moltenmetal containment into which rotatable degasser impellers project fromabove. The vessel may be used for batch processing, or it may be part ofa metal distribution system attached to metal conveying vessels. Ingeneral, the vessel may be any refractory metal containment vesselpositioned within a metal casing. The vessel may also be designed as arefractory ceramic crucible for containing large bodies of molten metalfor transport from one location to another. All such alternative vesselsmay be used with the exemplary embodiments of the invention.

EXAMPLES

Tests were carried out on a test piece of refractory material havingG-mat® web incorporated into the surface. The test piece was subjectedto thermal cycling to determine if it would delaminate, and was thensubjected to destructive testing to see if the web would hold a crackedpiece of refractory together. The results showed that the test piece didnot delaminate and the cracked piece did indeed hold together.

What is claimed is:
 1. A method of making a reinforced refractory vessel or vessel section, the method comprising: providing a mold having an intended shape of the vessel or vessel section; creating a slurry of a castable refractory material capable of forming a cast refractory body; lining at least one internal surface of the mold with a web of metal wires, the metal wires being overlaid with openings formed therebetween, wherein the web of metal wires comprises at least two overlying web sections, one of the at least two overlying web sections comprising a woven matrix of metal wires for providing structural reinforcement to the refractory material and another of the at least two overlying web sections comprising a non-woven matrix of metal wires including a plurality of metal wires overlying one another in a random fashion; introducing the slurry into the mold while causing the slurry to penetrate the openings; allowing the slurry to set to form the vessel or vessel section incorporating the web at an outer surface thereof; and removing the vessel or vessel section from the mold, wherein the non-woven matrix of metal wires defines a plurality of openings having an average width in a range of 50 μm to 350 μm and a plurality of convoluted paths across a thickness of the non-woven matrix for resisting penetration of the slurry through the non-woven matrix of metal wires.
 2. The method of claim 1, further comprising vibrating the mold before the slurry sets to facilitate penetration of the slurry into the openings of the web.
 3. The method of claim 1, further comprising pressurizing the mold before the slurry sets to facilitate penetration of the slurry into the openings of the web.
 4. The method of claim 1, further comprising vibrating and pressurizing the mold before the slurry sets to facilitate penetration of the slurry into the openings of the web.
 5. The method of claim 1, wherein the web of metal wires is lined on all parts of the at least one internal surface of the mold up to at least a horizontal level, wherein the horizontal level corresponds to a maximum intended surface height of molten metal within the vessel or vessel section.
 6. The method of claim 1, wherein a thickness of the metal wires of the woven matrix is greater than a thickness of the metal wires of the non-woven matrix.
 7. The method of claim 1, wherein the at least two overlying web sections are joined to each other.
 8. The method of claim 1, wherein the non-woven matrix is positioned closer to the outer surface of the vessel or vessel section than the woven matrix.
 9. The method of claim 1, wherein the woven matrix is positioned closer to the outer surface than the non-woven matrix.
 10. The method of claim 1, wherein the woven matrix has openings with an average width greater than an average width of openings in the non-woven matrix.
 11. The method of claim 1, wherein an average width of the openings in the woven matrix is in a range of 0.5 mm to 10 mm.
 12. The method of claim 1, wherein an average width of the openings in the woven matrix is in a range of 1 mm to 10 mm.
 13. The method of claim 1, wherein an average width of the openings in the non-woven matrix is in a range of 50 μm to 150 μm.
 14. The method of claim 1, wherein an average width of the openings in the non-woven matrix is about 100 μm.
 15. The method of claim 1, wherein the metal wires are made from a metal which resists attack by molten metal conveyed by the vessel or vessel section.
 16. The method of claim 1, wherein the metal wires are made from a metal selected from the group consisting of stainless steel, titanium, Ni—Cr based alloys, and Fe—Cr—Al based alloys.
 17. The method of claim 1, wherein the vessel or vessel section is an elongated trough or trough section with a cavity forming a channel extending from one longitudinal end of the cast refractory body to another end thereof.
 18. The method of claim 1, wherein the vessel or vessel section has an upper surface and a channel that is open at the upper surface.
 19. The method of claim 1, wherein the vessel or vessel section completely encloses a channel except at a first longitudinal end and a second longitudinal end. 